1. Field of the Invention
The invention relates to an electric motor and an electric unit including the electric motor.
2. Discussion of Background
There is a conventional electric oil pump device that is formed by assembling together an oil pump that circulates fluid (oil) and an electric motor that drives the oil pump. As such an electric oil pump device, Japanese Patent Application Publication No. 2006-274921 (JP 2006-274921 A) suggests an electric oil pump device in which an electric motor and an oil pump are arranged side by side along the direction of the central axis of the oil pump and accommodated together in a common housing.
The electric oil pump device has a structure in which bearings are arranged at respective end portions of a motor shaft to provide support at two positions. Hence, the motor shaft becomes long, and a member that supports the bearing disposed on the opposite side of the motor shaft from the oil pump is required. Therefore, in order to reduce the length of a motor shaft to obtain a more compact electric oil pump device, Japanese Patent Application Publication No. 2010-116914 (JP 2010-116914 A) suggests an electric oil pump device in which a motor shaft is supported at one axial position in a cantilever manner by a bearing device in a housing.
In an electric motor used in the electric oil pump device or in an electric power steering system, whirling of a motor shaft may become large due to, for example, runout, backlash or eccentricity between a stator and a rotor of the electric motor, or an attraction force generated by unbalance between the stator and the rotor and therefore vibrations or abnormal noise of the electric motor may be generated. When bearings are arranged at respective end portions of a motor shaft to reduce vibrations and abnormal noise of an electric motor, it is necessary to accurately perform centering of the inner periphery of a stator and centering of a rotor that is supported by the bearings at the respective end portions of the motor shaft.